Flow-rate switch

ABSTRACT

A flow-rate switch particularly suited for use in detecting variations in flow rates for fluids flowing through conduits of pressurized systems characterized by the utilization of a magnetically responsive circuit switching device seated within a tubular housing and a ring magnet concentrically disposed about the housing adapted to be repositioned in opposite directions along the housing for effecting circuit switching operations in response to changes in flow rates, a feature of the switch being the employment of a flow-responsive and variably positioned pintle disposed about said housing, within the path of the fluids, supporting the magnet for displacement relative to said switching device for repositioning the ring magnet relative to said switching device to effect switching operations as variation in flow rates occur.

United States Patent [72] Inventors T. 0. Paine Administrator of the National Aeronautics and Space Administration in respect to an invention 01; George P. Gale, Orange, Calif. 92667 [21] Appl. No. 860,492 [22] Filed Sept. 24, 1969 [45] Patented Jan. 4, 1972 [54] FLOW-RATE SWITCH 4 Claims, 4 Drawing Figs.

[52] [1.8. Ci. ..200/81.9 M, 3 35/205 [51] Int. Cl li0lh 35/40 [50] Field of Search ZOO/81.9 M, 83.6, 81.9; 335/205, 206, 207

[56] References Cited UNITED STATES PATENTS 2,892,051 6/1959 Mdore ZOO/81.9 M 1,941,695 1/1934 Ki1gour..... 200/819 X 2,310,504 2/1943 Aubert 200/819 M 2,791,657 5/1957 Bloxsom et a1. ZOO/81.9 M 2,826,754 3/1958 Carigrtan 200/81 .9 X

3,342,959 9/1967 Breunich 200/83 (.6) 3,510,816 5/1970 Bagg ZOO/81.9 M X FOREIGN PATENTS 1,154,117 6/1969 Great Britain ZOO/81.9 M

Primary Examiner-Robert K. Schaefer Assistant Examiner-Robert A. Vanderhye Attorneys-.1. H. Warden, Monte F. Mott and G. T. McCoy ABSTRACT: A flow-rate switch particularly suited for use in detecting variations in flow rates for fluids flowing through conduits of pressurized systems characterized by the utilization of a magnetically responsive circuit switching device seated within a tubular housing and a ring magnet concentrically disposed about the housing adapted to be repositioned in opposite directions along the housing for effecting circuit switching operations in response to changes in flow rates, a feature of the switch being the employment of a flow-responsive and variably positioned pintle disposed about said housing, within the path of the fluids, supporting the magnet for displacement relative to said switching device for repositioning the ring magnet relative to said switching device to effect switching operations as variation in flow rates occur.

Space Act of 1958, Public Law 85-668 (72 Stat. 435; 42 USC BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to flow-rate switches, and more particularly to a flow-rate switch adapted to respond to changes in rates of flow for fluids conducted through pressurized systems.

2. Description of the Prior Art The prior art includes numerous switching devices adapted to respond to changes in flow rates, fluid pressures and the like for initiating various circuit switching functions. Frequently, such devices employ spring-loaded and magnetically responsive circuit switching devices adapted to be actuated in response to magnetic fields established as magnets are displaced along a path extending adjacent thereto. However, these devices often are limited to use with relatively low pressure systems. Where such switches are employed as full-flow devices in flow interrupting dispositions within a body of a stream of fluid flowing under relatively high pressures, difficulty in adjusting the sensitivity of the switch often is encountered, as the switches tend to be insensitive to normally occurring changes in system flow rates. On the other hand, where the switching devices are coupled in an auxiliary or bypass system, difficulty in obtaining accurate results is experienced. Consequently, the switches heretofore available have not fully satisfied existing needs for highly reliable and simplified flow-rate switches which readily are adjustable for detecting relatively small variations in flow rates, while being substantially insensitive to system surges.

OBJECTS AND SUMMARY OF THE INVENTION This invention overcomes many of the aforementioned difficulties through the use of a full-flow, flow-rate switch, including an adjustably biased, reciprocably mounted, magnetbearing pintle having a tapered external surface coaxially associated within an internally tapered, fluid metering orifice formed in the housing of the switch and disposed in coaxial alignment with an input conduit for a stream of fluid, and including therein a bleeder for reducing erratic switching initiated by system surges, and an adjustable fluid bypass system for accommodating fine adjustment in achieving accurate circuit switching functions as pressures are varied within the system.

Accordingly, an object of the instant invention is to provide an improved flow-rate switch.

Another object is to provide an improved full-flow, flowrate switch adapted to be employed for detecting relatively small changes in flow rates for fluids flowing within pressurized hydraulic systems.

Another object is to provide an improved flow-rate switch which utilizes pressurized fluid in achieving a friction-free,

pressure-balanced, repetitive operation in detecting variations in flow conditions.

These together with other objects and advantages will become more readily apparent by reference to the following description and claims in light of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 4 is a diagrammatic view of an electrical circuit with which the switch of FIGS. 1 through 3 may be employed.

DESCRIPTIONOF THE PREFERRED EMBODIMENT Turning now to FIG. 1, therein is illustrated a switch embodying the principles of the present invention. The switch includes a housing 10 so coupled through conduits 12, within a pressurized system as to receive a full-flow delivery of pressurized streams of fluids. lllustratively, the switch is utilized in controlling the oil supply for a hydrostatic bearing operating under 1,500 P.S.I.

With particular reference to FIG. 2, the housing 10 includes a first elongated bore 15 which extends therethrough and defines an elongated fluid-confining pressure chamber 16. Extending from the bore 15, normal to the chamber, there is a second bore 18 which communicates with the chamber and serves as a fluid discharge conduit for the housing 10. The bore 15 also includes an internally threaded input orifice 19 into which is mated an externally screw-threaded fitting 20 of a suitable design. Preferably, the fitting is of a generally tubular configuration and includes an internally threaded portion 22, which serves to receive therein an externally threaded male fitting 24 which serves to couple the bore 15 with the conduit 12, whereby the chamber 16 is, at its input end, coupled with an input conduit 12. Where desired, a sealing of the fitting 20 relative to the housing 10 may be achieved through the use of a suitable device, such as, for example, an O-ring 25.

The fitting 20 also includes a tubular portion defining an elongated throat 26 terminating in an internally tapered annulus 28. The annulus serves as a fluid delivery orifice for delivering fluid, under pressure, from the pressurized system to the chamber 16. Seated in the chamber there is an axially displaceable pintle 30 having a terminal portion 32 extended through the annulus 28 and into the throat 26 of the fitting 20. The terminal portion of the pintle 30 includes an externally tapered surface terminating in a transverse pressure face 33. This face is arranged in a flow interrupting position relative to fluid delivered through the orifice 28 and serves to deliver forces developed by the flow to the pintle. The pintle 30 is adapted to be axially displaced relative to the internal surfaces of the orifice 28 for causing the tapered surfaces to dictate the flow of fluid delivered therethrough to the chamber 16. The pintle also includes a multiple dimensioned, stepped bore extending axially therethrough defining an open-ended chamber 34 terminating in a tubular conduit 36 of a reduced diameter, which extends from the chamber through the pressure face 33 for establishing communication therebetween.

Slidingly received within the elongated chamber 34 is an elongated, coaxially arranged, circuit housing 38 of a generally tubular configuration. The circuit housing rigidly is supported at one end by the switch housing 10, while the opposite end thereof is extended into the chamber in a manner such that the pintle 30 operatively is coupled in a telescoping relationship therewith. Also, as a practical matter, communication between the chamber 34 of the pintle 30 and the chamber 16 of the housing 10 is maintained between the adjacent surfaces of the circuit housing 38 and the chamber 34 in order that fluid may freely be exchanged between the chamber 34 and the chamber 16 and a film of lubrication con tinuously established therebetween.

The circuit housing 38 is coupled with the switch housing 10 through a screw-threaded coupling block 40 of a sleevelike configuration. The coupling block is seated within an end portion 41 of the bore 15 opposite the orifice l9, and includes an externally threaded male portion 42 mated with internal threads 43 provided therewithin. The distal end of the coupling block 40 also is provided with an internally threaded female portion 44 which serves to receive therein an externally threaded end portion 46 of the housing 38 in a manner such that the circuit housing is extended through the block 40 into a concentric relationship with the chamber 16. If desired, the housing 38 and block 40 may be sealed in a mated relationship by an O-ring 48.

It should readily be apparent that the housing 38 may be adjustably displaced, relative to the chamber 16, simply by applying torque to the housing for causing the housing screwthreadably to advance through the block 40. As a practical matter, the adjusted position of the housing 38, relative to the block 40, operatively is maintained through a lock nut 52 which also is screw-threadably received by the portion 46 of the housing 38.

Within the block 40, in concentric relationship with its male portion 42, there is provided a spring receiving chamber 53. Within this chamber there is disposed a helical spring 54 which circumscribes the adjacent end of the pintle 30 and is seated on the pintles adjacent external surface in a manner such that the spring continuously urges the pintle 30 in displacement away from the coupling block. Consequently, it should be appreciated that as the flow rate of the fluid delivered through the throat 26 increases the pintle is driven in displacement against the bias of the spring 54. However, as the flow rate decreases, the force of the spring 54 serves to overcome the applied force of the fluid and drives the pintle toward a seated disposition relative to the delivery orifice 28.

As a practical matter, the fluid flowing through the conduits 12 of the system normally experiences surges in flow due to various operative conditions of the ambient environment. The effects which such surges have on the axial displacement of the pintle are damped through a capillary tube 58 seated in the tubular conduit 36, as best illustrated in FIG. 2, having a blecder conduit 60 extending therethrough in a manner such that the chamber 34 always is in communication with the throat 26 of the fitting 20, whereby the fluid is permitted to be exchanged between the throat 26 and the chamber 34 as pressures rapidly are varied within the throat.

The throat 26 also is provided with an annular arrangement of radially extended openings 62. These openings, in practice, define fluid bypass ports for directing the flow of fluid from the throat through a bypass system. The bypass ports 62, in turn, are connected through an annular groove 64 with a bypass input channel 66 extending from the groove 64 to a bypass discharge channel 68. The channel 68 is interconnected with the discharge conduit 18 in a manner such that fluid delivered from the throat 26 through the ports 62 is discharged from the housing 10, in order that fluid pressures applied to the pintle 30, at the pressure face 33, be accurately maintained within a selected range of pressures. Furthermore, by providing an annular arrangement of ports, pressures are caused to be mutually opposed as they act against the pintle for thereby reducing the probability of encountering pressure initiated binding of the pintle.

Since in practice, the quantity of fluid which is permitted to bypass the tapered portion 32 of the pintle 30 serves to dictate the level of pressure applied to the face 33, the extent of reciprocating displacement which operatively is imposed upon the pintle 30 is dictated in part by the quantity of fluid being bypassed. Therefore, an externally threaded metering pin 70 is seated for axial displacement, in a suitably threaded seat 72, in a coaxial relation with the bypass input channel 66. By axially adjusting the position of the metering pin 70, relative to the channel 66, the quantity of fluid delivered through the bypass system may readily be varied to control the extent of displacement for the pintle 30, at any selected flow rate.

Within the housing 38 there is a plurality of axially displaced reed switches 74. Each of the reed switches is of a design which includes a pivotally supported bridging component 75, FIG. 4, formed of a material suitable for biasing the component to a normally closed position. While the number of switches may be varied, as desired, a pair of switches, including a first pair of contacts 76 and a second pair of contacts 78, is particularly suited for use in controlling fluid flow. As illustrated, the pair of switches 74 electrically are connected within an electrical circuit including an actuator 80 having therein a pair of solenoids 82 coupled with the switches 74 and adapted to respond to an interruption of the circuit at the switches. Of course, it should readily be apparent that the particular circuit within which the switches 74 are coupled may be varied as found desirable under given operative conditions.

For achieving a switching function for the reed switches 74, each component includes a member 84 of a suitable material coupled therewith and adapted to be displaced in the presence of a magnetic field. While a magnetically initiated displacement of the bridging component 75 may be employed for closing associated circuits, as a practical matter, it is preferred that the bridging components respond, under the influence of a magnetic field, to effect an interrupting of the associated circuits.

In order to initiate displacement of the bridging components 75, a suitable ring magnet 86 is seated on the pintle 30 in a circumscribing relation to a portion of the chamber 34 and adapted to be displaced with the pintle 30 relative to the housing 38. In practice, the magnet is supported between a suitable collar 88 and the spring 54, whereby the magnet is retained in a fixed operative disposition relative to the chamber 34. It should be apparent that the materials from which the pintle 30, circuit housing 38 and spring 54 are fabricated are compatible with the purposes and function of the flow-rate switch in order to preclude establishment of undesired fields of magnetic flux. Since such materials are readily available and may be varied as desired, a detailed description is omitted. However, it is to be understood that the materials are such that as the pintle 30 is displaced, the field of magnetic flux of the magnet 86 serves to effect a pivotal displacement for the bridging components 75, whereby an opening of the contacts of each of the switches 74 is achieved as the ring magnet is advanced in a given direction to a position in which the magnet and switch become concentrically related.

As a practical matter, the switches 74 are supported within the housing 38 by a plurality of beamlike connectors 92 which retain the switches 74 at selected locations. Each of the connectors 92, in turn, extends in a cantilevered fashion from a base 93 formed in a screw-threaded plug 94. The plug is screw-threaded into the open end of the housing 38 and serves to seal the open end thereof. The plug 94, of course, is of any suitable material, with the base 93 being so designed as electrically to insulate the connectors 92 in order to accommodate a conduction of an electrical current therethrough.

While various means, including brackets and the like may be employed in supporting and coupling the housing 10 in an operative disposition within the system, it has been found that the screw-threaded fitting 24 serves as an adequate support for joining the housing 10 with the input conduit 12, while a fitting 96 of similar design serves quite satisfactorily in coupling the discharge conduit 18 with the adjacent conduit 12. However, it should be appreciated that the operative environment dictates the manner in which the housing is supported.

OPERATION It is believed that in view of the foregoing description, the operation of the device will be readily understood, however, it will be briefly reviewed at this point. With the flow-rate switch assembled and mounted in the manner heretofore described, the switch electrically is coupled with an actuator 80. As a practical matter, the actuator circuit may be coupled with a flow control valve, not shown, in a manner such that should pressure maintained within the system fall below a predetermined value, the contacts 76, as shown in H0. 4, are opened for thus effecting an opening of the control valve and in the event the flow rate exceeds a predetermined value, the con tacts 78 are opened so that the control valve is closed for reducing the flow rate.

Coarse adjustment of the flow-rate switch is effected simply by displacing the housing 38, including the plug 94, relative to the block 40, while fine adjustment is achieved by manipulating the metering pins 70, relative to the bypass input channel 66, for thus establishing the quantity of fluid which is delivered through the bypass system to the discharge conduit 18, whereby the levels of pressure developed within the throat 26 and applied to the pressure face 33 are selectively controlled.

With the device appropriately adjusted, the pressure of the fluid flowing through the fitting acts against the pressure face 33. In the event the fluid flow is sufficient to achieve a displacement of the pintle 30, against the bias of the spring 54, the ring magnet 86 advances towards the switch contacts 78 for effecting a pivotal displacement of the associated bridging element 75, whereupon an opening of the associated circuit is achieved. If the flow decreases, the spring 54 is rendered effective for displacing the pintle 30 in an opposite direction. As the magnet 86 is positioned adjacent to the pair of contacts 76, the associated bridging element 75 is pivotally displaced, spacing the contacts and opening the associated circuit, whereupon a further control function is initiated. The extent of displacement of the pintle, of course, is proportional to the established flow rates and therefore is controlled through the adjustment of the metering pin 70. However, in the event system surges are encountered, the capillary bleeder conduit 60 is rendered effective for exchanging fluid between the chamber 34 and the throat 26 for thus obviating an occurrence of an erratic switching function.

In view of the foregoing, it should readily be apparent that the present invention provides a high-pressure flow-rate switch which is readily adjustable to function at selected flow rates for effectively achieving selected switching functions in a full-flow, high-pressure environment.

Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention.

What is claimed is:

l. A flow switch comprising:

A. a switch housing;

B. means defining within the switch housing a tubular bore including a fluid inlet port and a fluid discharge port, whereby a stream of fluid having a variable flow rate can be established within the housing;

C. an encapsulated, magnetically responsive reed switch supported in a fixed relationship with said housing, including a pivotal element electrically coupled with a given electrical circuit adapted to be actuated for modifying the circuit in response to an application of a field of magnetic flux to said switch;

D. an actuator disposed within said bore for applying a field of magnetic flux to said switch including,

i. an elongated, axially displaceable pintle having a transverse pressure face positioned to communicate with a stream of fluid established within said housing,

ii. means defining within said pintle an elongated cavity for receiving therewithin said reed switch,

iii. a permanent magnetic of an annular configuration seated on said pintle in a concentric relationship therewith,

' iv. support means operatively supporting said pintle for axial displacement relative to said switch, including an elongated fitting having an axial bore defining a throat extended therethrough and seated within said fluid input port in a concentric relationship therewith, means defining within the throat an internal surface of a frustoconical configuration extended in a coaxial relationship with said tubular bore and adapted to receive a terminal portion of said pintle, means defining within the fitting a plurality of radially extended, fluid bypass ports circumscribing the terminal portion of the pintle, and means defining a bypass channel disposed in communication with said bypass ports and the fluid discharge port, whereby the pintle is adapted to be displaced in a first direction, under the influence of forces applied to said pressure face as the rate of fluid flow through said housing is increased, and

v. biasing means operatively coupled with said pintle acting in opposition to said forces for displacing said pintle in a second direction as the rate of fluid flow through said housing is decreased; and

E. surge damping means operatively associated with said ac-' tuator for dissipating the effects of surge in the rates of flow, including means defining a continuously open conduit extending through said pressure face and communicating with said inlet port and said elongated cavity of said pintle, whereby a passage of fluid from said inlet port to said cavity continuously is accommodated.

2. The flow-rate switch of claim 1 wherein the pintle is provided with an external surface conforming to a frustoconical configuration adapted to seat within the internal surface of said fitting, whereby a metering orifice is established therebetween.

3. The switch of claim 2 further including adjusting means comprising:

A. a threaded coupling securing said reed switch with said switch housing for accommodating an axial adjustment of the switch relative to said elongated cavity; and

B. an adjustable needle valve, including a metering pin and a metering orifice disposed within said bypass channel and adapted to be adjusted for controlling flow rates through saidchannel, whereby a control of operative displacement for said pintle is achieved.

4. A flow-rate switch comprising:

A. a switch housing including an elongated bore extending therethrough and defining therewithin a tubular chamber;

B. means defining within the chamber an input port adapted to be coupled with an associated fluid conduit having therein fluid flowing at a variable flow rate;

C. an internally tapered axial bore defining within the input port a fluid metering orifice through which a flow of fluid to said chamber operatively is established;

D. an elongated pintle displaceably disposed within said chamber having an externally tapered end portion terminating in a transverse pressure face defining a metering pin axially received within said orifice adapted to be displaced in response to increasing rates of flow for fluid flowing through said orifice;

E. means defining an axial bore extending through said pintle and including a first terminal segment defining a surge damping capillary structure communicating with said orifice disposed at one end of the chamber, and a second terminal segment defining an elongated, open-end cavity near the opposite end of said chamber;

F. a ring magnet externally supported by said pintle in circumscribing relationship with the open-end cavity and adapted to establish therein a magnetic field;

G. biasing means acting against said pintle operatively coupled between said housing and said pintle for continuously urging the pintle in displacement toward said orifice whereby the pintle is caused to be displaced by said biasing means in response to decreasing rates of flow for fluid flowing within said orifice;

H. a tubular circuit housing telescopingly received within said open-end cavity;

I. adjustable coupling means adjustably coupling the circuit housing with said switch housing in a manner such that the magnet is caused to be repositioned relative to the circuit housing as the pintle is displaced in response to variations in rates for fluid flowing within said orifice;

a plurality of magnetically responsive switch elements electrically coupled with an associated circuit and pivotally supported within the circuit housing adapted pivotally to be displaced in response to the force of the magnetic field established by said magnet for interrupting the associated circuit as the pintle is displaced; and K. a fluid bypass system including a plurality of fluid bypass ports fonned within said orifice, a bypass channel coupling said bypass ports with the discharge port, and an adjustable needle valve arranged within the bypass channel, between said bypass ports and said discharge port, whereby the flow of fluid from said conduit is selectively diverted from said orifice at selected rates for thus controlling the displacement of said pintle. 

1. A flow switch comprising: A. a switch housing; B. means defining within the switch housing a tubular bore including a fluid inlet port and a fluid discharge port, whereby a stream of fluid having a variable flow rate can be established within the housing; C. an encapsulated, magnetically responsive reed switch supported in a fixed relationship with said housing, including a pivotal element electrically coupled with a given electrical circuit adapted to be actuated for modifying the circuit in response to an application of a field of magnetic flux to said switch; D. an actuator disposed within said bore for applying a field of magnetic flux to said switch including, i. an elongated, axially displaceable pintle having a transverse pressure face positioned to communicate with a stream of fluid established within said housing, ii. means defining within said pintle an elongated cavity for receiving therewithin said reed switch, iii. a permanent magnetic of an annular configuration seated on said pintle in a concentric relationship therewith, iv. support means operatively supporting said pintle for axial displacement relative to said switch, including an elongated fitting having an axial bore defining a throat extended therethrough and seated within said fluid input port in a concentric relationship therewith, means defining within the throat an internal surface of a frustoconical configuration extended in a coaxial relationship with said tubular bore and adapted to receive a terminal portion of said pintle, means defining within the fitting a plurality of radially extended, fluid bypass ports circumscribing the terminal portion of the pintle, and means defining a bypass channel disposed in communication with said bypass ports and the fluid discharge port, whereby the pintle is adapted to be displaced in a first direction, under the influence of forces applied to said pressure face as the rate of fluid flow through said housing is increased, and v. biasing means operatively coupled with said pintle acting in opposition to said forces for displacing said pintle in a second direction as the rate of fluid flow through said housing is decreased; and E. surge damping means operatively associated with said actuator for dissipating the effects of surge in the rates of flow, including means defining a continuously open conduit extending through said pressure face and communicating with said inlet port and said elongated cavity of said pintle, whereby a passage of fluid from said inlet port to said cavity continuously is accommodated.
 2. The flow-rate switch of claim 1 wherein the pintle is provided with an external surface conforming to a frustoconical configuration adapted to seat within the internal surface of said fitting, whereby a metering orifice is established therebetween.
 3. The switch of claim 2 further including adjusting means comprising: A. a threaded coupling securing said reed switch with said switch housing for accommodating an axial adjustment of the switch relative to said elongated cavity; and B. an adjustable needle valve, including a metering pin and a metering orifice disposed within said bypass channel and adapted to be adjusted for controlling flow rates through said channel, whereby a control of operative displacement for said pintle is achieved.
 4. A flow-rate switch comprising: A. a switch housing including an elongated bore extending therethrough and defining therewithin a tubular chamber; B. means defining within the chamber an input port adapted to be coupled with an associated fluid conduit having therein fluid flowing at a variable flow rate; C. an internally tapered axial bore defining within the input port a fluid metering orifice through which a flow of fluid to said chamber operatively is established; D. an elongated pintle displaceably disposed within said chamber having an externally tapered end portion terminating in a transverse pressure face defining a metering pin axially received within said oRifice adapted to be displaced in response to increasing rates of flow for fluid flowing through said orifice; E. means defining an axial bore extending through said pintle and including a first terminal segment defining a surge damping capillary structure communicating with said orifice disposed at one end of the chamber, and a second terminal segment defining an elongated, open-end cavity near the opposite end of said chamber; F. a ring magnet externally supported by said pintle in circumscribing relationship with the open-end cavity and adapted to establish therein a magnetic field; G. biasing means acting against said pintle operatively coupled between said housing and said pintle for continuously urging the pintle in displacement toward said orifice whereby the pintle is caused to be displaced by said biasing means in response to decreasing rates of flow for fluid flowing within said orifice; H. a tubular circuit housing telescopingly received within said open-end cavity; I. adjustable coupling means adjustably coupling the circuit housing with said switch housing in a manner such that the magnet is caused to be repositioned relative to the circuit housing as the pintle is displaced in response to variations in rates for fluid flowing within said orifice; J. a plurality of magnetically responsive switch elements electrically coupled with an associated circuit and pivotally supported within the circuit housing adapted pivotally to be displaced in response to the force of the magnetic field established by said magnet for interrupting the associated circuit as the pintle is displaced; and K. a fluid bypass system including a plurality of fluid bypass ports formed within said orifice, a bypass channel coupling said bypass ports with the discharge port, and an adjustable needle valve arranged within the bypass channel, between said bypass ports and said discharge port, whereby the flow of fluid from said conduit is selectively diverted from said orifice at selected rates for thus controlling the displacement of said pintle. 